Press backspace to undo creating new list item

[leoluk]

In many outliners, if you create a new outline item such as:

- existing item[enter]
- [cursor is here now]

...then pressing backspace returns you to the previous item:

- existing item [cursor is here now]

In SB, you currently have to press backspace multiple times to remove the bullet point, indentation and the newline itself. It could be nice to be smarter about this.